factor of 2. At a depth of 113 m the shaft friction is 30 MN. Therefore, the safety factor on
uplift is 30/8, that is, nearly 4.
Checking the working stress on the steel,
For a wall thickness of 25 mm max. compressive stress == 170 Nmm^2This is 50% of the yield stress for high-tensile steel which is satisfactory for the easy
driving conditions. The thickness can be decreased to 16 mm in the lower 50 m of the pile.
Example 4.3
A building column carrying a dead load of 1100 kN and an imposed load of 300 kN is to be
supported by a single bored pile installed in firm to stiff fissured London Clay (Figure 4.43).
Select suitable dimensions and penetration depth to obtain a safety factor of 2 in total pile
resistance, or safety factors of 3 in end bearing and unity in shaft friction. Calculate the
immediate settlement at the working load.
A pile of 1 m diameter is suitable. A penetration depth of 13 m (12 m below cut-off level)
will be tried.
16 106
1
4
(1270(^2) 1 234 (^2) )
226 Resistance of piles to compressive loads
Undrained shear strength, kN/M^2
0
0
20
40
60
80
100
120
140
160
Undrained shear strength
versus depth
Ultimate resistance versus depth for 1220 m OD
tubular steel pile with closed end
Shaft friction
Total pile capacity
Average cu
cu
(gsub = 0.65Mg/m^3 )
s9vo= 0.26
Base resistance
Depth below sea bed (m)
100 200 300 0 1020304050
Ultimate pile capacity, MN
Penetration for working load
of 16MN (safety factor = 2)
Figure 4.42